As further background, numerous devices exist in the prior art to fill an intervertebral space following removal of all or part of the intervertebral disc in order to prevent disc space collapse and to promote fusion of the adjacent vertebrae within the disc space. Some of the earlier-developed devices stabilize the spinal column with a metal plate or rod spanning the affected vertebrae and fusion is promoted by disposing bone material between the adjacent vertebrae.
Several types of metal intervertebral spacers, including hollow spinal cages, are also currently being used to stabilize the spinal column. Fusion of adjacent vertebrae utilizing these spacers is typically promoted by filling the cages with an osteogenic material. Although metal plates, rods and spacers served the purpose of stabilizing the spinal column, the metallic devices remained as a permanent foreign body after fusion occurs. Attempts at alleviating this problem have included utilizing devices composed entirely of bone or having minimal metallic components.
Besides becoming incorporated into the resultant fusion mass, intervertebral spacers composed entirely of bone or having minimal metallic components have other advantages. For example, bone allows excellent postoperative imaging because it does not cause scattering like metallic spacers. Stress shielding is avoided because bone grafts have a similar modulus of elasticity as the surrounding bone. However, many of these bone spacers do not have sufficient compressive strength to withstand the cyclic loads of the spine, and the supply of suitable bone starting materials for fabrication of the spacers is limited in several respects. Needs thus exist for additional strategies for fabricating spacers possessing sufficient compressive strength to withstand the compressive loads of the spinal column and which provide flexibility in the use of existing bone stocks. The present invention address these needs.